# A beam of red light has twice the intensity as a second bean of the same color

1. May 11, 2008

### looi76

1. The problem statement, all variables and given/known data
A beam of red light has twice the intensity as a second bean of the same color. Calculate the ratio of the amplitude of wave.

2. Relevant equations
$$intensity \propto (amplitude)^2$$

3. The attempt at a solution
$$1^{st} \mbox{ beam} = 2I$$
$$2^{nd} \mbox{ beam} = I$$

I don't know if this step is correct and I don't know what to do next?!

2. May 11, 2008

### Antenna Guy

$$I_1=2 I_2$$

$$\frac{I_1}{I_2}=2$$

What can you do to the above relation (given your relevant equation) to convert it to a ratio of amplitudes?

Regards,

Bill

3. May 11, 2008

### looi76

$$intensity \propto (amplitude)^2$$

So, it will be $$1:4$$ ?

4. May 11, 2008

### Defennder

No, start off by expressing both intensities I = kA^2. Then compare the ratio of each amplitude to the other.

5. May 11, 2008

### Antenna Guy

No. Try what Defennder suggested to see why.

Regards,

Bill